diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index c440d6466004..cd01fe81fd88 100644
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -9307,10 +9307,11 @@ class LibvirtConnTestCase(test.NoDBTestCase):
                                 CONF.image_cache_subdirectory_name)
         instance = objects.Instance(**self.test_instance)
         disk_info_byname = fake_disk_info_byname(instance)
-        disk_info = disk_info_byname.values()
 
-        # Give the ephemeral disk a non-default name
         disk_info_byname['disk.local']['backing_file'] = 'ephemeral_foo'
+        disk_info_byname['disk.local']['virt_disk_size'] = 1 * units.Gi
+
+        disk_info = disk_info_byname.values()
 
         with test.nested(
             mock.patch.object(libvirt_driver.libvirt_utils, 'fetch_image'),
@@ -9338,8 +9339,7 @@ class LibvirtConnTestCase(test.NoDBTestCase):
 
             verify_base_size_mock.assert_has_calls([
                 mock.call(root_backing, instance.flavor.root_gb * units.Gi),
-                mock.call(ephemeral_backing,
-                          instance.flavor.ephemeral_gb * units.Gi)
+                mock.call(ephemeral_backing, 1 * units.Gi)
             ])
 
     def test_create_images_and_backing_disk_info_none(self):
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index dacccf1bf1b5..05bfc1a22825 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -6608,12 +6608,19 @@ class LibvirtDriver(driver.ComputeDriver):
                                                  instance_disk,
                                                  CONF.libvirt.images_type)
                 if cache_name.startswith('ephemeral'):
-                    image.cache(fetch_func=self._create_ephemeral,
-                                fs_label=cache_name,
-                                os_type=instance.os_type,
-                                filename=cache_name,
-                                size=info['virt_disk_size'],
-                                ephemeral_size=instance.flavor.ephemeral_gb)
+                    # The argument 'size' is used by image.cache to
+                    # validate disk size retrieved from cache against
+                    # the instance disk size (should always return OK)
+                    # and ephemeral_size is used by _create_ephemeral
+                    # to build the image if the disk is not already
+                    # cached.
+                    image.cache(
+                        fetch_func=self._create_ephemeral,
+                        fs_label=cache_name,
+                        os_type=instance.os_type,
+                        filename=cache_name,
+                        size=info['virt_disk_size'],
+                        ephemeral_size=info['virt_disk_size'] / units.Gi)
                 elif cache_name.startswith('swap'):
                     inst_type = instance.get_flavor()
                     swap_mb = inst_type.swap